Xdebug

Xdebug
Daily helper and professional debugger

TobiasSchlitt <toby@php.net>

PHP@FrOSCon 2009

2009-08-23

Tobias Schlitt (PHP@FrOSCon 2009) Xdebug 2009-08-23 1 / 36

About me

Tobias Schlitt <toby@php.net>
PHP since 2001
Freelancing consultant
Qualiﬁed IT Specialist
Studying CS at TU Dortmund
(expect to ﬁnish this year)
OSS addicted
PHP
eZ Components
PHPUnit


Overview

1 About Xdebug

2 Installation

3 Development goodies

4 Tracing

5 More features...


Outline

1 About Xdebug

2 Installation


4 Tracing

5 More features...


Why a debugger?

“I don’t need a debugger”
There is no bug free code
Make live easier, use a debugger!
“var dump(), print r() and echo are suﬃcient”
In a lot of cases they are
Debugging with them is slow and a lot of work
“Using a debugger = using an IDE”
No, but you can


What is Xdebug?

Open Source debugger for PHP
PHP (Zend Engine) extension
Works (at least) on Linux, Mac and Windows
About 5 years old
Current stable version: 2.0.3
Created and maintained by Derick Rethans
http://xdebug.org


Xdebug features

Enhance daily work with PHP
Trace PHP program runs
Proﬁle PHP applications
Analyze code coverage (e.g. PHPUnit)
Remote-debugging with an external client
Including break-points, stepping, . . .


Outline

1 About Xdebug

2 Installation
Installation
Conﬁguration


4 Tracing

5 More features...


Via PEAR

Easiest way to install
Working PEAR assumed:
$ pear install pecl/xdebug
PEAR Installer performs necessary steps:
1 Download source
2 Compiling module
3 Copying module to destination
After that: Add module to php.ini
Only on *nix systems


Manual

Compile by hand
Typical PHP module compile process
wget h t t p : / / xdebug . o r g / l i n k . php ? u r l=xdebug201
t a r −x z f xdebug − 2 . 0 . 2 . t g z
cd xdebug − 2 . 0 . 2
phpize
. / c o n f i g u r e −−enable −xdebug
−−w i t h −php−c o n f i g =/ u s r / b i n / php−c o n f i g
make
cp m o d u l e s / xdebug . s o /<m o d u l e p a t h >/xdebug . s o

Only on *nix systems


Windows

Download binary module from
http://xdebug.org
http://pecl4win.php.net/ext.php/php_xdebug.dll
Copy module to modules directory


Add module to php.ini

Not a “normal” extension
Add to php.ini:
zend extension = ”/path/to/xdebug.so”
On Windows: zend extension ts
For debug builds zend extension debug
Check $ php −v or phpinfo() ;


Common pitfalls

extension dir directive does not take eﬀect!
Binary modules (Windows) do not work with PHP debug builds
−−enable−versioning prevents loading
Other zend-extensions interfere with Xdebug


Conﬁguration

Huge variety of options
Most shown later, some not
Overview: http://xdebug.org/docs/all_settings
Most options adjustably with ini set () at runtime, except for
xdebug.extended info
xdebug. proﬁler ∗


Outline

1 About Xdebug

2 Installation

Error messages
Dumping variables
Inﬁnity
Useful functions

4 Tracing

5 More features...


Getting started

Install module
Switch it on
Tweak some settings
Work as usual


Error messages

PHP error messages not very useful
Sometimes poor error location
Almost no info on aﬀected data
No info on code context
Xdebug enhances that for you!


Warnings

Functions producing warnings

f u n c t i o n openSomeFile ()
{
r e t u r n o p e n M y F i l e ( ’ / p a t h / t o / f i l e ’ , ’ Reason t o open f i l e .
’ , a r r a y ( 2 3 , 4 2 , ’ Random d a t a . ’ ) ) ;
}

f u n c t i o n o p e n M y F i l e ( $path , $ r e a s o n , $ d a t a )
{
r e t u r n fopen ( $path , ’ r ’ ) ;
}

function performOperationOnFile ( $ f i l e )
{
r e t u r n f r e a d ( $ f i l e , 1024 ) ;
}


Warnings

Triggering a warning

require once ’ w a r n i n g / f u n c t i o n s . php ’ ;

f u n c t i o n performAComplexOperation ()
{
$ f i l e = openSomeFile () ;
return performOperationOnFile ( $ f i l e ) ;
}

echo p e r f o r m A C o m p l e x O p e r a t i o n ( ) ;


Warnings

Live
Let’s look what it does


Errors

Producing an exception

r e q u i r e o n c e ’ /home/ d o t x p / dev /PHP/ e z c o m p o n e n t s / t r u n k / Base / s r c
/ b a s e . php ’ ;

function a u t o l o a d ( $className )
{
r e t u r n ezcBase : : a u to l o ad ( $className ) ;
}

$pop3 = new e z c M a i l P o p 3 T r a n s p o r t ( ” l o c a l h o s t ” ) ;


Errors

Live


var dump()

Using var dump()
Everyone does it
There is nothing bad about it
var dump() in the browser sucks
Xdebug enhances var dump()

Live


Inﬁnite loops

Endless recursions
Extremely hard to ﬁnd
Script just times out . . . or worse!
Xdebug can protect you
Note: Not from endless runs of loops!


Inﬁnite recursion

Producing an inﬁnite recursion

f u n c t i o n d o u b l e F a c u l t y ( $num )
{
/∗
i f ( $num < 3 )
{
r e t u r n $num ;
}
∗/
r e t u r n $num ∗ d o u b l e F a c u l t y ( $num − 2 ) ;
}

echo d o u b l e F a c u l t y ( 10 ) ;


Inﬁnite recursion

Live


Useful functions

xdebug [en/dis ] able ()
Manually switch stack traces on or off
xdebug call [ class /function/ file / line ]()
Get the call point of the currently running function
xdebug dump superglobals()
Dump super-globals as specified by INI setting


Useful functions

xdebug get declared vars ()
Returns an array containing the names of all variables in the current
scope
xdebug get function stack ()
Returns the function stack trace as an array
xdebug get stack depth()
Get the current depth in the function stack
Note: Includes also create a level!


Useful functions

xdebug time index()
Returns the seconds since script run start


Declared vars

Getting declared variables

f u n c t i o n f o o ( $a , $b )
{
g l o b a l $c ;
$d = ’ I am l o c a l ’ ;
var dump ( x d e b u g g e t d e c l a r e d v a r s ( ) ) ;
}

$c = ’ I am g l o b a l ’ ;

f o o ( 2 3 , 42 ) ;


Declared vars

Live


Stack depth

Retrieving stack level

echo ” S t a c k d e p t h i n ” . FILE . ”: ” .
x d e b u g g e t s t a c k d e p t h ( ) . ” nn” ;

function foo ()
{
echo ” S t a c k d e p t h i n ” . FUNCTION . ”: ” .
x d e b u g g e t s t a c k d e p t h ( ) . ” nn” ;
bar () ;
}

i n c l u d e ’ s t a c k d e p t h / d e e p e r s t a c k . php ’ ;

echo ” C a l l i n g f o o ( ) from ” . FILE . ” nn” ;
foo () ;


Stack depth

Live


Outline

1 About Xdebug

2 Installation


4 Tracing

5 More features...


What is tracing?

Check control flow of application
Correct function calls
Correct data
Does input data produce correct workflow?
Traces always depend on input data
Almost impossible to create traces for every possible control flow


Tracing

Some developers trace like this:
echo ” Here I am ! ! ! ” ;
// . . .
echo ”Now I ’m h e r e ! ! ! Something i s : ” ;
var dump ( $ s o m e t h i n g ) ;

Works well in small scripts
Horror in larger apps / libraries
Debugging like this is a sh**load of work
Almost impossible with 3rd party code


Tracing with Xdebug

By functions:
xdebug start trace ()
xdebug stop trace ()
Automatically (php.ini)
xdebug.auto trace = ”1”
Cannot be set via ini set () !


Tracing example

A simple trace

f u n c t i o n d o u b l e F a c u l t y ( $num )
{
i f ( $num < 3 )
{
r e t u r n $num ;
}
r e t u r n $num ∗ d o u b l e F a c u l t y ( $num − 2 ) ;
}

x d e b u g s t a r t t r a c e ( ’ t r a c e s /60 s i m p l e t r a c e . x t ’ ) ;

echo d o u b l e F a c u l t y ( 10 ) ;


Tracing example

Live


Notes on tracing

Never trace in production!
Tracing is extremely slow!
grep & friends help a lot
Tuning conﬁguration makes traces more usable
More information through Xdebug mean
Slower performance
Higher memory consumption


Outline

1 About Xdebug

2 Installation


4 Tracing

5 More features...


Proﬁling

Which code takes which time?
Find bottle necks in code
Check your database queries and setup ﬁrst!


Code coverage

Mostly used in testing
Which code is not covered by a test?
PHPUnit can utilize this
http://www.phpunit.de


Remote debugging

Integrate Xdebug into your IDE
Komodo IDE
Eclipse


The end

Thank you for listening!
Are there any questions left?
I hope you learned what you expected?
Contact me: Tobias Schlitt <toby@php.net>
Slides will be up on Slideshare


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